This invention relates to an internal combustion engine, and in particular to an internal combustion engine wherein protective covers for protecting various attachments such as an air-intake system or an exhaust system, specifically protective covers for protecting a carburetor, an air cleaner and a muffler are attached to an engine body.
Conventionally, a small air-cooled two-cycle gasoline engine (hereinafter referred to as an internal combustion engine) has been commonly employed as a power source for a portable working machine such as a bush cutter. FIG. 6 shows a schematic front view of such a conventional internal combustion engine. Referring to FIG. 6, an internal combustion engine 51 comprises a fuel tank 52 horizontally mounted at a lower portion of the internal combustion engine 51, an engine body 55 which is disposed over the fuel tank 52 and comprises a crankcase 54 and a cylinder 53 mounted integral with and perpendicular to the upper portion of the crankcase 54, a muffler 58 attached to one side of the engine body 55, and a combination of an air cleaner 57 and a carburetor 59 attached to the other side of including the cylinder 53. The outer side of each of the engine body 55, the muffler 58 and the combination of the air cleaner 57 and the carburetor 59, are covered respectively by protective covers 61, 63 and 65, which are formed of a molded thin plate designed to cover the outer appearance of each device, each protective cover being spaced apart from the surface of each device and fastened to the engine body 55.
In particular, the protective cover 65 for the muffler 58 and the protective cover 61 for both the air cleaner 57 and the carburetor 59 are arranged symmetrically about the engine body 55 so as to keep a good balance with each other in external appearance.
Additionally, the protective cover 65 for the muffler 58 is provided with many slit-like through-holes 67 for radiating heat generating from the muffler 58 itself, whereas the protective cover 61 for both the air cleaner 57 and the carburetor 59 is not provided with such through-holes water drops and the like are required to be prevented from entering into the air cleaner 57 and the carburetor 59. Thus, the protective cover 61 for both the air cleaner 57 and the carburetor 59 is formed of a flat thin plate molded into a cap-like shape having on its inner surface a plurality of stiffening ribs for the reinforcement thereof or for fastening the protective cover to the engine body 55.
Siner the stiffening ribs are concurrently formed on the inner surface of a thin protective cover at the occasion of molding the protective cover for both the air cleaner 57 and the carburetor 59 by making use of a synthetic resin, the external appearance of the protective cover is more likely to be distorted due to a thermal shrinkage in this molding process, thereby giving rise to a problem that it becomes one of the causes for producing a defective product.
A recoil handle (not shown) for a recoil starter (not shown) of the internal combustion engine is disposed near the protective cover covering both the air cleaner 57 and the carburetor 59, so that it is sometimes observed that an operator pulls the recoil handle of the recoil starter of the internal combustion engine with his one hand for starting the engine, while placing his other hand on the protective cover covering both the air cleaner 57 and the carburetor 59. In that case, the protective cover may be deformed or sometimes cracked due to the pressure of the operator's hand placed on the protective cover covering both the air cleaner 57 and the carburetor 59.
Moreover, these protective covers are constructed such that only the protective cover 65 for the muffler 58 is provided with many slit-like through-holes 67 out of all of the protective covers covering the muffler 58 or covering both the air cleaner 57 and the carburetor 59 which are arranged symmetrically about the engine body 55 as mentioned above, i.e. such through-holes 67 are not formed at all in the protective cover 61 covering both the air cleaner 57 and the carburetor 59, so that the external appearances of these protective covers are rendered unbalanced in design.